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Re: double fault -> PAGE_KERNEL flagged memory
- From: Tom Zanussi <zanussi at us dot ibm dot com>
- To: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- Cc: "Stone, Joshua I" <joshua dot i dot stone at intel dot com>, Tom Zanussi <zanussi at us dot ibm dot com>, michel dot dagenais at polymtl dot ca, systemtap at sources dot redhat dot com
- Date: Tue, 22 Nov 2005 09:12:15 -0600
- Subject: Re: double fault -> PAGE_KERNEL flagged memory
- References: <CBDB88BFD06F7F408399DBCF8776B3DC05A8FB95@scsmsx403.amr.corp.intel.com> <20051122140021.GA3907@Krystal>
Mathieu Desnoyers writes:
> I suspect that your double fault may come from the systemTAP logging code. Do
> you have an instrumentation point in any fault handler ?
>
> For Tom : can you flag the RelayFS buffer memory PAGE_KERNEL instead of
> GFP_KERNEL ? Otherwise, it leads to page faults when accessing those pages when
> accessed for the first time (seen with LTTng).
It already is PAGE_KERNEL. The page faults you see with relayfs are
vmalloc page faults i.e. minor faults that just update the kernel part
of the current process's page table with the buffer pages.
Anyway, systemtap doesn't use relayfs unless -b (bulk) is specified on
the command line, so unless that's the case, it can't be relayfs
causing the problem.
tom